Pressurized fluids stored in containers (cans or vessels) are used in a wide field of applications. Sprayable foams are used for several industrial applications as well as by hobbyists. One well known example of sprayable foam is polyurethane foam. Polyurethanes are, among others, used in high resiliency flexible foam seating, rigid foam insulation panels, microcellular sprayable foam seals and gaskets, durable elastomeric wheels and tires, electrical potting compounds, Spandex fibers, carpet underlay, hard plastic parts.
At present, existing sprayable foam formulations are one and two component PU foams (OCF=One Component Foams; TCF=Two Component Foams) in aerosol cans and/or pressure vessels. A PU foam formulation comprise of a mixture of polyols, diisocyanates, liquefied gases as blowing agents, and several additives. These foams provide excellent mechanical properties and outstanding thermal insulation. Therefore these are widely used in the construction field for thermal and sound insulation and fixation of door frames and others. These froths are cured by the reaction of the isocyanate terminated prepolymers with moisture.
In two component foams (TCF), both a polyol/additive/blowing agent and a NCO/additive/blowing agent mixture are made in separate cans. Both mixtures are blended upon spraying. In the OCF manufacturing process, at the first stage an aerosol can is filled of with a mixture of a polyol blend, isocyanate, different additives and physical blowing agent like Liquefied Petroleum Gases (LPG) and DME (Dimethylether). The pre-polymerization reaction occurs inside the can: the polyol is reacted with isocyanate which is abundantly in excess present.
At the second stage, while dispensing, the liquid prepolymer leaves the can and starts to expand to a low density froth by vaporization of the physical blowing agent. Once exposed to the air, in the third stage, and in the presence of a chemical blowing agent (water), the reaction between water and the excess isocyanate will occur to form unstable carbamic acid which immediately decomposes into an amine and carbon dioxide, which will assure a second expansion of the foam.
A disadvantage of the above described process is that isocyanates are toxic. MDI, Methylene Diphenyl Diisocyanate, is the isocyanate most commonly used in the production of the PU foam. This compound, although the least hazardous of the isocyanate groups, is still toxic, harmful by inhalation or ingestion, and also via skin contact. In addition, the compound is flammable and can also be explosive.
The elaborate use of the pressurized fluids brings along some safety concerns. It is of utmost importance to use PU foams with a high froth or cure rate, so the foam is suitable for spray-on applications and for filling holes and cavities. The use of environmentally friendly blowing agents as well as non-harmful catalysts has become an important and urgent issue in the synthesis of PU foam. One Component Foams (OCF's) nowadays contain free monomeric crude MDI, which are critical with respect to toxicological and environmental implications. Isocyanates are even suspected of causing cancer and exposure to free, noncured isocyanates is dangerous. The present invention is a key resource to underpin these developments.
A proposed solution to avoid the toxic effect of isocyanates is the use of Alpha Silane terminated PU prepolymers (STP's). A well-known example is Soudafoam SMX® which is isocyanate-free fixing foam. Soudafoam SMX® is a moisture-curing system and performs best on moderately moistened porous surfaces. On non-porous surfaces, the best performance is achieved when the surface is dry and when the joint/cavity is shallow. In the case of a deeper joint/cavity it is better to fill the gap in two layers, with a drying/curing time in between.
Another example of the incorporation of silane to avoid the toxic effect of isocyanate is presented in JP2000026648. JP'648 presents a process for preparing foams without using isocyanates and strongly acidic substances. A composition is proposed containing i) an organic compound having a carboncarbon double bond, ii) a compound having an SiH group and iii) a blowing agent and/or a compound having an OH group.
Although isocyanate-free, the use of PU foams based on Alpha Silane terminated PU prepolymers in aerosol cans has several drawbacks, such as high viscosity, slow curing, some crack formation and a rather high cost.
EP1798255 discloses a process for preparing precursor mixtures of polymer foam to be packed in pressurized vessels and or aerosol cans. The polymer foam can be either a polyester foam, a foam based on cyclocarbonate oligomers and primary amine oligomers, or a foam based on acrylic oligomers. Biodiesel is included as latent hardener arid/or extender and/or liquid filler in polyurethane formulations, more particularly One Component Foams precursor mixtures. The improved formulation avoid long-term deterioration of flexibility and mechanical strength of the foam.
Given the above drawbacks of existing sprayable PU foams, it is a main object of the present invention to provide optimized PU foam with respect to production cost, high shelf-life, ease of handling and efficiency.
It is a particular object of the invention to provide sprayable foam that allows fast curing. The curing of the unsaturated polyester resin and the acrylates oligomers is performed via a free radical crosslinking mechanism. This makes the foams suitable for spray-on applications and for filling holes and cavities. Spraying of the foam is thus simple and user friendly. Further, by using fast curing PU foam, contact with free non-cured isocyanates is avoided.
It is a further object of the present invention to provide sprayable foam that is safe for human's health. Although MDI is the least hazardous of the isocyanate groups, it is still toxic and harmful by inhalation or ingestion, and also through skin contact. By combining the MDI with oligomers having reactive end groups, the toxic isocyanates groups are shielded and health safety is guaranteed.
It is also an object of the present invention to provide a sprayable foam that is environmentally friendly without loss of overall characteristics of the foam. The use of environmentally friendly blowing agents as well as non-harmful catalysts has become an important and urgent issue in the synthesis of PU foam. By shielding the toxic isocyanates, the risk of release of toxic gases, especially upon catching fire or explosion, is reduced.
The present invention meets the above objects by using acrylated terminated urethane and polyester oligomer sprayable foam in accordance with the present invention.